Through protein and DNA sequence analyses, much information on the primary structure of membrane bound proteins has accumulated over the past several years. It is proposed to utilize this information to prepare antibodies reactive with defined portions of these molecules. This will be done by synthesizing 10-20 residue peptides that correspond to sections of the sequence of the membrane bound proteins. After coupling to a carrier protein, antisera to these peptides will be prepared. In the case of transplantation and other lymphocyte antigens, these antibodies will be used to define sites of cellular recognition and serological specificities. The feasibility of utilizing synthetic peptides as protective immunogenic and therapeutic reagents will also be investigated. In these cases, peptides corresponding to portions of viral or parasitic proteins will be used to seek protective immunity against infection or to treat infection. By using small, defined peptides, it is potentially possible to limit the side effects encountered with vaccines.